Fall 2008 Physics 101 Hour Exam 1(24 questions)

The grading button and a description of the scoring criteria are at the bottom of this page. Basic questions are marked by a single star *. More difficult questions are marked by two stars **. The most challenging questions are marked by three stars ***.

True-false questions are worth 2 points each, three-choice multiple choice questions are worth 3 points each, five-choice multiple choice questions are worth 6 points each. The maximum possible score is 108. The exam period was 90 minutes; the mean score was 76.3; the median score was 78. Click here to see page1 page2 page3 of the formula sheet that came with the exam.

QUESTION 1*

This and the following question concern the same physical situation.

Your car is stopped at the edge of a 14 m wide road. Your car can accelerate at 3.5 m/s2.

What is the shortest time for your car to cross the 14 m wide road?

(a)   1.0 s
(b)   2.8 s
(c)   9.8 s

QUESTION 2*

Suppose that you stall in the middle of the road, when the group of cars are 200 m away. What is the minimum braking acceleration magnitude necessary for them to come to a stop before they hit you?

(a)   3.6 m/s2
(b)   9 m/s2
(c)   9.8 m/s2

QUESTION 3**

This and the following two questions concern the same physical situation.

A box of mass mbox = 1 kg sits on a wheeled cart of mass mcart = 14 kg. The wheels roll freely (without friction). The coefficient of static friction between the box and the cart is μs = 0.4. You begin to push the cart horizontally.

What is the magnitude of the maximum static friction force on the box?

(a)   0.4 mbox g
(b)   0.4 mcart g
(c)   0.4 (mcart + mbox) g

QUESTION 4*

How much horizontal force can you exert on the cart before the box begins to slide?

(a)   147 N
(b)   58.8 N
(c)   40.0 N
(d)   19.6 N
(e)   3.14 N

QUESTION 5***

Suppose now that the friction coefficient between the box and the cart is zero. At t = 0 you start pushing the cart with a force F. What is the acceleration of the box abox at t = 0?

(a)   abox = 0
(b)   abox = F / mbox
(c)   abox = F / (mbox + mcart)

QUESTION 6*

This and the following three questions concern the same physical situation.

I shot an arrow in the air. The initial speed is 50 m/s, and the arrow is oriented at 45° to the horizontal. Neglect air resistance and assume the arrow started at the same height as the ground.

What is the arrow's vertical (y) acceleration just before it hits the ground?

(a)   +9.8 m/s2
(b)   0 m/s2
(c)   -9.8 m/s2

QUESTION 7*

What is the speed of the arrow just before it hits the ground?

(a)   30 m/s
(b)   40 m/s
(c)   50 m/s

QUESTION 8*

How far does the arrow go before it hits the ground?

(a)   144 m
(b)   201 m
(c)   255 m
(d)   301 m
(e)   355 m

QUESTION 9*

Suppose that the answer to the previous question is L. What would the answer be if the initial speed were 25 m/s?

(a)   L / 4
(b)   L / sqrt(2)
(c)   2 L

QUESTION 10***

An astronaut free falls toward the Earth at a distance of 3 Earth radii from the center of the Earth. What is his acceleration?

(a)   0.01 m/s2
(b)   0.11 m/s2
(c)   1.1 m/s2
(d)   9.8 m/s2
(e)   It is impossible to tell from the information given.

QUESTION 11**

This and the following question concern the same physical situation.

Three weights of mass M are hung from the ceiling using three ropes. The top on is hung directly from the ceiling, the second is hung below the first one, and the third one is hung below the second one.

Which one of the following is true?

(a)   The tension in the top rope is the same as that in the bottom rope.
(b)   The tension in the top rope is less than that in the bottom rope.
(c)   The tension in the top rope is more than that in the bottom rope.

QUESTION 12**

Suppose that the mass of the lowest weight was doubled. By what factor would the tension in the top rope increase?

(a)   1.33
(b)   1.5
(c)   2

QUESTION 13**

A box of mass m sits inside a funicular railway that is moving up and to the left at constant velocity V. Which one of the following is true about the apparent weight FN?

(a)   FN < mg
(b)   FN = mg
(c)   FN > mg

QUESTION 14*

A professor walking west at 1 m/s on Green St runs into a student bicycling south on Goodwin Ave at 5 m/s. What is their relative speed?

(a)   1 m/s
(b)   5 m/s
(c)   5.1 m/s
(d)   6 m/s
(e)   6.1 m/s

QUESTION 15*

This and the following question concern the same physical situation.

There is an ocean current of 7m/s from west to east. A cruise ship can move at the speed of 18 m/s relative to the water.

What is the speed v of the cruiser relative to the water in knots (1 knot = 1.852 km/hr)?

(a)   v = 10 knots
(b)   v = 15 knots
(c)   v = 25 knots
(d)   v = 35 knots
(e)   v = 50 knots

QUESTION 16***

If one wishes to go due north with this cruise ship on this current, what is the angle θ of the ship from north?

(a)   θ = 17°
(b)   θ = 19°
(c)   θ = 21°
(d)   θ = 23°
(e)   θ = 25°

QUESTION 17**

This and the following two questions concern the same physical situation.

A block of mass 15 kg sits in on a horizontal surface. The coefficient of kinetic friction between the block and the surface is μk. The x component of its velocity (which is parallel to the surface) is graphed below.

The position (x coordinate) of the block is graphed versus time. Which of the three graphs below is the correct one?

(a)
(b)
(c)

QUESTION 18*

What is the absolute value of the x-component of the acceleration at t = 1 s?

(a)   | ax | = 2.0 m/s2
(b)   | ax | = 3.0 m/s2
(c)   | ax | = 4.0 m/s2
(d)   | ax | = 5.0 m/s2
(e)   | ax | = 6.0 m/s2

QUESTION 19*

To maintain the velocity between 2 and 5 sec, you have to push the block horizontally in the positive x direction with a force of magnitude 85 N. What is the coefficient of kinetic friction μk?

(a)   μk = 0.13
(b)   μk = 0.29
(c)   μk = 0.58
(d)   μk = 2.9
(e)   μk = 5.8

QUESTION 20*

This and the following two questions concern the same physical situation.

A 70 kg person steps onto an elevator with a 10 kg dumbbell. While riding in the elevator, the person notices that the dumbbell actually weighs 11 kg on a scale.

What do you know about the direction the elevator is moving (its velocity)?

(a)   up
(b)   down
(c)   not enough information

QUESTION 21**

What is the magnitude of the force N on the person from the elevator floor? You may assume that he leaves the dumbbell on the floor and stands still relative to the floor.

(a)   F = 530 N
(b)   F = 690 N
(c)   F = 739 N
(d)   F = 755 N
(e)   F = 815 N

QUESTION 22**

What is the magnitude | a | of the acceleration of the elevator? Choose the closest answer.

(a)   | a | = 1.0 m/s2
(b)   | a | = 2.0 m/s2
(c)   | a | = 4.0 m/s2
(d)   | a | = 9.8 m/s2
(e)   | a | = 10.8 m/s2

QUESTION 23***

This and the following question concern the same physical situation.

There is an incline and a block of mass 20 kg on it as shown in the figure. The angle of the slope is 40°.

When the horizontal force F whose magnitude is 360 N is applied as shown in the figure, the block stays stationary on the slope. What is the magnitude of the normal force acting on the block from the slope?

(a)   150 N
(b)   231 N
(c)   250 N
(d)   331 N
(e)   382 N

QUESTION 24**

Then, oil is applied between the block and the inclined surface to make the surface frictionless. The horizontal force F = 360 N is still applied as in the figure. What is the magnitude of the acceleration of the block?

(a)   7.5 m/s2
(b)   8.6 m/s2
(c)   9.7 m/s2
(d)   10.8 m/s2
(e)   11.9 m/s2

Scoring of True-False (T,F) Questions:
• If you mark the correct answer, you get 2 points.
• If you mark the wrong answer or if you mark neither answer, you get 0 points.
Scoring of Multiple Choice I (a,b,c) Questions:
• If you mark the correct answer, you get 3 points.
• If you mark a wrong answer or if you mark none of the answers, you get 0 points.
Scoring of Multiple Choice II (a,b,c,d,e) Questions:
• If you mark one answer and it is the correct answer, you get 6 points.
• If you mark two answers and one of them is the correct answer, you get 3 points.
• If you mark three answers and one of them is the correct answer, you get 2 points.
• If you do not mark the correct answer, or if you mark more than three answers, or if you mark none of the answers, you get 0 points.